Instrumentation has been developed for the study of fluorescence or circular dichroism during exposure of biological samples to microwave radiation (2450 MHz, CW). Fluorescence experiments have shown that microwave radiation at SAR's of 10 and 200 mW/g had no effect on calcium binding to human erythrocyte membranes or on energy transfer between membrane bound probes and intrinsic tryptophan residues. Circular dichroism measurements have shown that spectrin molecules from human erythrocyte membranes may be affected by high microwave power levels (600 mW/g, SAR). These effects may result from differential intramolecular interactions with the oscillating electric field. Experiments utilizing these instruments will help to clarify reported microwave effects by examining them on a molecular basis. The studies have been extended to include the effects of microwave radiation on microtubular polymerization in vitro.